Method for casting conductor of a cage rotor of an induction motor and apparatus for casting the same

ABSTRACT

The invention relates to an apparatus for casting a conductor of a cage rotor of an induction motor. A rotor core (13) comprising a laminated steel sheets is housed in a recess portion of a casting mold, an upper end portion thereof is held by a holding portion (70) and molten metal is supplied into a plurality of slots formed in the rotor core, thereby forming a plurality of conductor rods and a pair of end rings connecting the ends of the conductor rods with one another. The holding portion (70) comprises a cup (72) and a cylinder (73), and an axial dimension of the cup (72) is selected in correspondence to an axial dimension of the rotor core (13) housed in the recess portion of the casting mold. Further, by using a double cylinder (77, 79) in the holding portion (70), a rotor having higher quality can be obtained. For this reason, the same conductor casting apparatus can be used for casting the conductor of the rotor having different axial lengths and qualities depending on specifications.

FIELD OF THE TECHNOLOGY

The present invention relates to a method for casting a conductor of acage rotor of an induction motor and an apparatus for casting the same.

BACKGROUND ART

When manufacturing a cage rotor which is used in an induction motor,there has been known a method for integrally forming conductor rods tobe disposed in a plurality of slots of a rotor core and end ringsconnecting each of the conductor rods at both ends in an axial directionby casting such as a die casting and the like. The conductor formingmethod mentioned above has an excellent productivity and can easily forma conductor having a desired shape, and further the method is suited forimproving the characteristic of the motor. For this reason, the methodhas been widely employed in particular for a compact induction motor. Amethod for manufacturing a conventional cage rotor of an induction motorwill be described with reference to a flow chart shown in FIG. 14 andschematic diagrams shown in FIG. 15(a), FIG. 15(b), FIG. 15(c) and FIG.15(d).

A cage rotor 12 is provided with a plurality of laminated steel sheets11 (FIG. 15(a)) which has a plurality of circumferential slots 44, andconductor rods 46 (FIG. 15(d)) extending through the slots 44 of thepiled up laminated steel sheets 11.

Then, a method for manufacturing the cage rotor 12 will be describedbelow with reference to the flow chart shown in FIG. 14.

First, a plurality of laminating steel sheet 11 are piled up and stackedso as to form the rotor core 12 by passing a hole formed in a center ofthe laminated steel sheet 11 through a fixed mandrel 90 (FIG. 15(b))(Step S11). Next, the thickness of the laminated material is adjusted bymeasuring the laminated thickness of the stacked rotor core 12 (StepS12). Then, as shown in FIG. 15(b), balance rings 92 are placed on anupper end and a lower end of the rotor core 12 and then those balancerings 92 and the rotor core 12 are tightened each other by fasteningportions 94 and 96 (Step S13 and FIG. 15(b))

Next, after pre-heating the rotor core 12 (Step S14), the rotor core 12is inserted into a metal mold. Then, molten metal such as aluminum andthe like is filled in the metal mold at a high speed and a highpressure. That is, a die casting is performed (Step S15). After themolten metal is solidified within the slot 44 of the rotor core 12, themandrel 90 is pulled out from the rotor core 12 (Step S16).

FIG. 15(d) shows a state that the mandrel 90 is pulled out from therotor core 12. In general, since the diameter of the mandrel 90 isselected to be smaller by a value d (a degree of play) than the diameterof the hole formed in the center of the laminated steel sheet 11, asshown in FIG. 15(c), the center holes of the plurality of laminatedsteel sheet 11 stacked to each other are not aligned with each other, asshown in FIG. 15(b) and FIG. 15(d), thereby forming an unevenness on theinternal side surface. This unevenness is leveled by later machining,thereby making easier the insertion of the rotor shaft. Further,sometimes, the outer surface of the rotor core 12 may be leveled byremoving the unevenness thereon.

However, in the method for casting the conductor of the rotor corementioned above, there are problems arising from number of kinds of,number of or performance of jigs necessary for casting the metal mold,the mandrel and the like, which affect forming efficiency and quality ofthe rotor core.

That is, when manufacturing induction motors for various outputspecifications, there arises a problem such that various kinds of metalmolds are necessary. In general, the output of the induction motor isdifferentiated by changing an axial length while keeping the diameter ofthe cage rotor constant. Therefore, the rotor cores having the samediameters but having different axial lengths are necessary for manykinds of output specifications. However, for different axial lengths ofthe rotor core, different metal molds (even if the diameters are thesame) are necessary. Accordingly, the different metal molds arenecessary for the induction motors having different outputspecifications, giving rise to the need of various kinds of metal molds.

Further, as to the mandrel too, there arises a problem such that aunique mandrel is necessary for the rotor core having a differentlength. In casting a rotor core, a mandrel system is generally known asmeans for fixing the laminated steel sheet piled up to each other. Inthe mandrel system, since the upper and lower ends of the laminatedsteel sheet in the axial direction are gripped by the fastening members,and the mandrel for fixing is used as a jig for applying a pressure forfixing, the different fixing mandrels are necessary for the differentkinds of rotor core differing in axial length. Further, since the fixingmandrel requires a long time for being removed, it is difficult to useone fixing mandrel in rotation for mass production of the rotor cores,so that the number of fixing mandrels corresponding to the number of therotor core to be cast will be needed. As a result, there arises aproblem that it is necessary to supply a number of fixing mandrels.

Further, in fixing the cast rotor core to the output shaft of theinduction motor, there is a problem such that the treatment for theinner periphery of the rotor core is necessary. In the case wherelaminated steel sheets is stacked on the mandrel so as to form the rotorcore, in general, there is a clearance (d in FIG. 15(c)) resulting froma gap between the sleeve diameter of the mandrel and the inner peripheryof the laminated steel sheet due to the operability of the stack, sothat the bore of the rotor core is hard to be aligned at a time. Whenmounting the rotor core to the outputted shaft of the induction motor,the rotor core is usually fixed by shrinkage fit. Accordingly, if therotor core is mounted without aligning the bore of the rotor core by theinner periphery treatment, the output shaft may be curved, or theinitial balance of the rotor may be adversely affected.

DISCLOSURE OF THE INVENTION

An object of the present invention is to reduce the kinds and number ofjigs such as metal molds, mandrels and the like necessary for casting,thereby improving the performances of the jigs and manufacturingefficiency and quality of the rotor core.

More particularly, an object of the invention is to provide a method andan apparatus for casting a conductor of a cage rotor of an inductionmotor designed for reducing the kinds of the metal mold necessary forcasting the cage rotors coping with many kinds of output specifications.Another object is to reduce the kinds of the mandrel necessary therefor.Further, another object is to reduce the time required for operationusing the mandrel and reduce the number of the mandrels necessarytherefor. Further, another object is to provide a method and anapparatus for casting the conductor of the cage rotor of the inductionmotor, which do not need the bore working of the rotor core.

In order to achieve the above objects, in accordance with the presentinvention, there is provided an apparatus for casting a conductor of acage rotor of an induction motor comprises a casting mold provided witha recess portion for receiving a rotor core formed by piling up steelsheets and restraining a motion of the rotor core in a radial direction,and a holding portion moving toward an end surface of the rotor corehoused in the recess portion of the casting mold by means of drive meansand acts on the end surface so as to fix the axial motion of the rotorcore, wherein molten metal is poured into a plurality of slots formed inthe rotor core fixed by the recess portion and the holding portion so asto form a plurality of conductor rods and a pair of end ringscommunicating the ends of the conductor rods with one another, wherein amoving amount of the holding portion can be adjusted in correspondenceto an axial length of the rotor core.

Alternatively, the holding portion is structured to comprise a cylindermoving toward the end surface of the rotor core by means of the drivemeans and a pressing member connected to the cylinder and acting on theend surface of the rotor core by a motion of the cylinder, and thepressing member is selected so that it may have an axial dimensioncorresponding to the axial length of the rotor core and is mounted onthe cylinder. Otherwise, the casting mold may be designed to be commonwhile the cylinders and pressing member may be replaced to cope with theaxial length of the core.

Preferably, the pressing member comprises a cup-shaped member having anaxial dimension corresponding to the axial length of the rotor core, orcomprises a combination of a cup-shaped member having a constant axialdimension and a spacer having an axial dimension corresponding to theaxial length of the rotor core. Further, for the rotor required to havea higher casting quality, a double cylinder can be employed for enablingapplication of localized pressure. Even when the double cylinder isemployed, all the function of the single cylinder mentioned above can berealized.

Preferably, the apparatus for casting the conductor is provided with afirst mandrel as an accessory whose thermal expansion rate is largerthan that of the steel sheets constituting the rotor core, whose axialdimension is not shorter than that of the rotor core and which has asleeve portion provided with heating means in its inside, and the firstmandrel is heated by the heating means after being inserted into thecentral opening of the rotor core prior to being received within therecess portion of the casting mold, whereby an unevenness of the innerperiphery of the central opening of the rotor core is leveled by thethermal expansion of the sleeve.

Preferably, the apparatus for casting the conductor is provided with asecond mandrel as an accessory which comprises a shaft portion having anouter diameter allowable for being inserted into the central opening ofthe rotor core, a supporting portion disposed on one end of the shaftportion and a shoulder portion having a diameter larger than the outerdiameter of the shaft portion disposed on the other end of the shaftportion. When the second mandrel is inserted into the central opening ofthe rotor core received in the recess portion of the casting mold, andthe casting is completed, the rotor core is removed out of the recessportion of the casting mold together with the second mandrel by beingheld by the supporting member of the second mandrel.

Preferably, the casting mold is provided with a plurality of air ventsin an axial direction on the inner surface of the recess portion whichhouses the rotor core.

Further, in accordance with the invention, there is provided a methodfor casting a conductor of a cage rotor of an induction motor comprisessteps of, (a) laminating steel sheets to a predetermined thickness bypassing a central opening of the steel sheets through a sleeve portionof a mandrel, (b) leveling an unevenness of inner periphery of a centralopening of the laminated steel sheets occurred during laminating processby the effect of thermal expansion of said sleeve resulting from beingheated, (c) pressing said laminated steel sheets in the axial directionand temporarily fixing the outer periphery thereof so as to form therotor core, (d) housing said rotor core in the recess portion of thecasting mold formed in the conductor casting apparatus, (e) adjusting anaxial dimension of the holding portion or a stroke of the holdingportion acting on an axial end of said rotor core, to axial dimension ofsaid rotor core, and (f) forming a plurality of conductor rods and apair of end rings communicating ends of the conductor rods with oneanother by supplying molten metal into a plurality of slots formed inthe rotor core which is held by said holding portion.

It is preferable to add between the above Steps (c) and (d) a step ofinserting a mandrel provided with a shaft portion having an outerdiameter allowable for being inserted into the central opening of therotor core, an end portion with a supporting portion disposed at an endof the shaft portion and a shoulder portion having a diameter largerthan the outer diameter of said shaft portion disposed at the other endof the shaft portion, and to add after said Step (f) a step forremoving, by using said mandrel, the rotor, with which a plurality ofconductor rods and a pair of end rings are formed in the rotor core,from the casting mold.

According to the invention, in a method for casting a conductor of acage rotor of an induction motor and an apparatus for casting the same,kinds and number of jig such as metal molds, mandrels and the likenecessary for casting can be reduced, a performance of the jigs can beimproved and manufacturing efficiency and quality of rotor core can beimproved.

Further, in casting cage rotors to cope with various outputspecifications, the kinds of the metal mold and the mandrel necessaryfor casting can be reduced, time required for operation using themandrels and the number of the mandrel necessary for casting can bereduced. Still further, casting the conductor of the cage rotor of theinduction motor can be performed without requiring bore working of therotor core.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of an apparatus forcasting a conductor of a cage rotor of an induction motor in accordancewith the present invention;

FIG. 2(a) is a schematic view showing a state in which a rotor core ishoused in a recess portion of a casting mold of the apparatus forcasting the conductor of the cage rotor in accordance with the inventionand is fixed by a holding portion, and

FIG. 2(b) is a schematic view showing a state in which a moving strokeof a piston of the holding portion is enlarged by the fact that a rotorcore having a short axial dimension is housed in the recess portion ofthe casting mold of the conductor casting apparatus shown in FIG. 2(a);

FIG. 3(a) is a schematic view showing that the cage rotor is formed byshrinkage fitting the rotor core having conductor rods formed by theconductor casting apparatus shown in FIG. 2(a) and an end ringconnecting the ends of the conductor rods with one another, to the shaftfor fixation,

FIG. 3(b) is a cross sectional view as seen from a b--b section of FIG.3(a), and FIG. 3(a) is a partial cross sectional view as seen from ana--a section of FIG. 3(b);

FIG. 4 is a flow chart showing a series of steps comprising a step offorming the rotor core by laminating the steel sheets, a step of forminga conductor portion (the conductor rod and the end ring) in the rotorcore by the conductor casting apparatus and a step of removing the rotorin which the conductor portion is formed on the rotor core from theconductor casting apparatus;

FIG. 5(a) is a schematic view showing a state in which the steel sheetsare laminated,

FIG. 5(b) is a schematic view showing a state in which the mandrel isinserted into the central opening of the laminated steel sheets,

FIG. 5(c) is a top plan view showing the state of FIG. 5(b),

FIG. 5(d) is a schematic view showing a state in which a thermalexpansion is effected to the mandrel shown in FIG. 5(b) and

FIG. 5(e) is a top plan view showing the state of FIG. 5(d);

FIG. 6(a) is a schematic view showing a state in which the mandrel shownin FIG. 5(d) is cooled;

FIG. 6(b) is a top plan view showing the state of FIG. 6(a);

FIG. 6(c) is a schematic view showing a state in which the mandrel ispulled out from the state of FIG. 6(a); and

FIG. 6(d) is a perspective view of the mandrel;

FIG. 7 is a schematic view showing one form of the mandrel to beinserted into the rotor core for carrying the rotor core to theconductor casting apparatus and removing the rotor core, in which theconductor rod and the end rings are formed, from the conductor castingapparatus;

FIG. 8(a) and FIG. 8(b) are schematic views explaining that an axialdimension of a cup portion of a holding portion for holding the rotorcore by acting on the end portion of the rotor core is changed incorrespondence to a length of the axial dimension of the rotor corehoused in the recess portion of the casting mold of the conductorcasting apparatus;

FIG. 9(a) and FIG. 9(b) are schematic views explaining that an axialdimension of a spacer disposed between a cup portion and the end portionof the rotor core is changed in accordance with the axial dimension ofthe rotor core housed in the recess portion of the casting mold of theconductor casting apparatus;

FIG. 10 is a schematic view explaining that the conductor of the rotorprovided with a balance ring is formed by the conductor castingapparatus;

FIG. 11 is a schematic view showing an apparatus for casting a conductorwhich is provided with a cup for locally applying pressure to an endring forming portion disposed on a side opposite to a sprue, in additionto the cup acting on the end surface of the rotor core housed in therecess portion of the casting mold so as to hold the rotor core, therebyenabling the cups to be driven independently by the respectivecylinders, and showing that the mandrel shown in FIG. 2(a) is employedfor the rotor core in the conductor casting apparatus;

FIG. 12 is a schematic view showing that a mandrel including a sleevehaving the same length as the axial length of the rotor core is employedin place of the mandrel in the form shown in FIG. 11;

FIG. 13(a) and FIG. 13(b) are schematic views showing a state in whichthe mandrel shown in FIG. 2(a) and FIG. 2(b) are replaced by the mandrelshown in FIG. 12;

FIG. 14 is a flow chart showing a series of steps of a conventionalembodiment comprising a step of forming the rotor core by laminating thesteel sheets, a step of forming a conductor portion (the conductor rodand the end ring) in the rotor core by the conductor casting apparatusand a step of removing the rotor in which the conductor portion isformed in the rotor core from the conductor casting apparatus; and

FIG. 15(a) is a schematic view showing a state in which the steel sheetsare laminated;

FIG. 15(b) is a schematic view showing a state in which the mandrel isinserted into the central opening of the laminated steel sheets to formthe conductor and unevenness of the central opening of the rotor coreexisting at this time;

FIG. 15(c) is a schematic view showing a state in which a gap is formedbetween the mandrel and the rotor core; and

FIG. 15(d) is a schematic view showing a state in which the unevennessremains with the central opening of the rotor without being removed evenafter the conductor is formed and the mandrel is pulled out.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of an apparatus for casting a conductor of a cage rotor ofan induction motor in accordance with the present invention will bedescribed below with reference to FIG. 1, FIG. 2(a) and FIG. 2(b).

A conductor casting apparatus 10,is provided with a casting mold 18having a recess portion 14 for housing a rotor core 12 of a cage rotorand a sprue 16 communicating with the recess portion 14. The recessportion 14 and the sprue 16 are connected by a runner 20 substantiallysymmetrically branched in two directions. The casting mold 18 is dividedinto a fixed mold 24 and a movable mold 26 by a parting plane 22extending in a vertical direction (in a vertical direction in FIG. 1).The movable mold 26 is movable either way in a horizontal direction (ina horizontal direction shown by an arrow A in the drawing) with respectto the fixed mold 24. Therefore, the casting mold 18 is designed to beseparated and joined in a radial direction of the rotor core 12.

The metal mold comprises the fixed mold 24 and the movable mold 26.Further, the fixed mold 24 and the movable mold 26 respectively comprisemain molds 24a and 26a, and sub-molds 24b and 26b structured to beinserts for the main molds 24a and 26a. The recess portion 14, the sprue16 and the runner 20 are recessed towards the fixed mold 24 and themovable mold 26 from the parting plane 22 in a manner such that theyhave substantially the same shapes so that when the both molds 24 and 26are joined, a single casting mold cavity and a single sprue system areconstituted. In this case, the recess portion 14, the sprue 16 and therunner 20 are formed in the sub molds 24b and 26b.

The sprue 16 is disposed immediately below the recess portion 14, andthe runner 20 is opened to a peripheral wall of a lower end of therecess portion 14. A receiving portion 28 is formed in the main molds24a of the fixed mold 24 and the main mold 26a of the movable mold 26respectively disposed below the sprue 16, and an injection front end(not shown) of a casting machine such as a die casting machine or thelike is mounted on the receiving portion 28. Further, a plurality of airvent (a first air vent 15 and a second air vent 17) for allowing gas toescape from a cavity during casting are formed along the parting plane22 in the fixed mold 24 and the movable mold 26. The air vents extendthrough the main molds 24a and 26a and the sub molds 24b and 26b, oneend of each vent opening to an upper peripheral wall or an innerperipheral wall of the recess portion 14 and the other end thereofopening to the open air through chill vents (a first chill vent 30 and asecond chill vent 31) formed in the main molds 24a and 26a.

The movable mold 26 is provided with a plurality of guide pins 32projecting from the parting plane 22 of the main mold 26a and a coresupporting rail 34 projecting from the parting plane 22 of the sub mold26b. Further, the fixed mold 24 is provided with a guide groove 36 and arail receiving groove 38 which are recessed from the parting plane 22 atpositions corresponding to the positions of the guide pin 32 and thecore supporting rail 34. Still further, the movable mold 26 is providedwith a pushing sheet 40 and a plurality of pushing pins 42 for pushingout the rotor core 12, formed with the conductor, from the recessportion 14.

Next, the rotor core 12 of the cage rotor will be described below withreference to FIG. 3(a) and FIG. 3(b).

The rotor core 12 is constituted of a laminated body made of a magneticsteel sheet such as a silicon steel sheet 11 and the like, and isprovided with a conductor rod 46 formed within each of a plurality ofslots 44 formed axially extending along an outer peripheral portionhaving a substantially cylindrical shape, and a pair of end rings 48formed on both axial ends of the rotor core 12 to connect the pluralityof conductor rods 46 one another. The plurality of conductor rods 46 andthe pair of end rings 48 are integrally formed by a casting such as analuminum die casting and the like using a conductor casting machine 10.The rotor core 12 having the integrally formed conductor portion isfixed to a shaft 52 in a central cylindrical opening 50 by a shrinkagefit and the like to form a known cage rotor.

The rotor core 12 is disposed in the recess portion 14 of the castingmold 18 in a manner such that it is supported by a mandrel 54(hereinafter referred to as a simple mandrel) shown in FIG. 2(a). Thesimple mandrel 54 is provided with a shaft portion and a shoulderportion, the shoulder portion being disposed in a base of the lower endof the shaft portion and having a diameter larger than an outer diameterof the shaft portion, and is a jig for carrying the rotor core 12 byinserting the shaft portion into the open hole in the axial core portionof the rotor core 12 and supporting the lower end portion of the rotorcore 12 by means of the shoulder portion. It is sufficient for thesimple mandrel 54 to have at least a function for carrying the rotorcore 12, and the outer diameter of the shaft portion of the simplemandrel 54 needs to be determined so that a clearance can be providedfor allowing the insertion of the shaft portion into the rotor core 12.Further, the simple mandrel 54 has a lower end portion projectingdownward, and is engagedly inserted into a pair of guide projections 62of the core supporting rail 34 of the movable mold 26, whereby thesimple mandrel 54 and the rotor core 12 are slidably supported by thecore supporting rail 34. Still further, a ring-shape supporting memberfor moving the simple mandrel itself 54 or the simple mandrel and therotor core 12 supported thereby is provided on the upper end of thesimple mandrel 54.

The rotor core 12 supported, with its axis being kept vertical, by thesimple mandrel 54 is mounted on the core supporting rail 34 of themovable mold 26 as shown in FIG. 1 and FIG. 2(a).

When the rotor core 12 supported by the simple mandrel 54 is insertedinto the recess portion 14 of the movable mold 26, and the movable mold26 is moved to be joined to the fixed mold 24, the rotor core 12 ishoused in a predetermined position within the recess portion 14, withthe outer peripheral surface thereof being substantially closely andevenly in contact with the peripheral wall of the recess portion 14. Inthis case, in the lower end region of the recess portion 14, a firstannular end ring cavity 64 for forming the end ring 48 is defined amongthe axial end surface of the rotor core 12, the outer peripheral surfaceof the shoulder portion of the base of the simple mandrel 54 and thewall surface of the recess portion 14. In a similar manner, in the upperend of the recess portion 14, a second annular end ring cavity 66 forforming the end ring 48 is defined among the axial end surface of therotor core 12, the outer peripheral surface of a cup 72 (describedlater) and the wall surface of the recess portion 14. The first end ringcavity 64 and the second end ring cavity 66 communicate with a pluralityof slots 44 of the rotor core 12.

The conductor casting apparatus 10 is further provided with a holdingportion 70 for fixing and holding the rotor core 12 within the recessportion 14 by bringing its end portion into contact with the upper endportion of the rotor core 12. The holding portion 70 is designed to becapable of moving and adjusting in the direction toward the end portionof the rotor core 12. The holding portion 70 shown in FIG. 2(a)comprises the cup 72 for holding, fixing and pressing the rotor core 12by being brought into contact with the upper end of the rotor core 12and a cylinder 73 for driving the cup 72. The movement of the holdingportion 70 toward the end portion of the rotor core 12 is controlled byadjusting the stroke length of the cylinder 73. In the case of FIG.2(a), since the axial dimension of the rotor core 12 is relatively long,the stroke of the cylinder is adjusted to be relatively short. In thecase of FIG. 2(b), since the axial dimension of the rotor core 12 isrelatively short, the stroke of the cylinder is adjusted to berelatively long.

When the cylinder 73 is moved towards the rotor core 12 side, the cup 72is brought into contact with the upper end of the rotor core 12 withinthe recess portion 14 so as to press the rotor core 12. As a result, therotor core 12 is held in a predetermined position within the recessportion 14 between the cup 72 and the core supporting rail 34.

Further, the axial end surface of the cup 72 defines the second end ringcavity 66, and applies pressure to the molten iron filled in the secondend ring cavity 66.

Next, a procedure for constructing the rotor core 12 by piling up thelaminated steel sheets 11, prior to the casting operation by means ofthe conductor casting apparatus 10, will be described below withreference to FIG. 5(a) to FIG. 5(e) and FIG. 6(a) to FIG. 6(d).

In order to stack the laminated steel sheets 11, a mandrel 80(hereinafter referred to as an open mandrel) as shown in FIG. 6(d) isused. The open mandrel 80 is provided with a sleeve portion 80a and ashoulder portion 80b for supporting the laminated steel sheets 11stacked to each other. A thermal expansion rate of the sleeve portion80a is larger than that of the laminated steel sheet 11, and the sleeveportion 80a has an axial length larger than the axial length of therotor core 12 formed by piling up. The open mandrel is provided withheating means such as a heater 82 and the like and cooling means such asa cooling pipe passage 84 and the like. When heated by the heater 82,the sleeve portion 80a expands in the radial direction and presses thelaminated steel sheets 11 along their inside peripheries so as tostraighten the inner peripheral surface of the rotor core 12. Further,when cooled by the cooling pipe passage 84, the diameter of the sleeveportion 80a is shrunk in its radial direction forming a gap between theouter peripheral surface of the sleeve portion 80a and the innerperipheral surface of the rotor core 12. As a result, the rotor core 12is opened forming so as to be pulled out from the open mandrel 80.

Next, a procedure for integrally forming the conductor portion on therotor core 12 by means of the conductor casting apparatus 10 having theabove structure will be described with reference to the flow chart shownin FIG. 4. In this procedure, the conductor casting is mainly dividedinto a process of constituting the rotor core 12 by the laminated steelsheets (a process A), a process of pre-heating the rotor core 12 (aprocess B) and a process of die casting the rotor core 12 in theconductor casting apparatus 10 (a process C).

In the process A, as shown in FIG. 5(b), first the laminated steel sheet11 (FIG. 5(a)) are provided with central openings and are passed by thesleeve portion 80a of the open mandrel 80 for enabling the laminatedsheets to be piled up (Step S1) to form the rotor core 12, and then theoverall thickness of the lamination is adjusted (Step S2). Theadjustment of the lamination thickness can be made by an automaticlamination thickness adjusting apparatus. The laminated steel sheet 11is not completely aligned leaving some unevenness as to the innerperipheral surface, as schematically shown in FIG. 5(b). The gap betweenthe laminated steel sheet 11 and the sleeve portion 80a of the mandrel80 is, for example, about 50 μm.

After forming the rotor core 12 by accumulating the laminated steelsheets 11, the heater 82 of the open mandrel 80 is operated to heat theopen mandrel 80 (Step S3). The open mandrel 80 and the rotor core 12 isexpanded by this heating. When the thermal expansion rate of the openmandrel 80 is set to be larger than the thermal expansion rate of thelaminated steel sheets 11, the outer peripheral surface of the sleeveportion 80a is brought into contact with the inner peripheral surface ofthe central hole of the laminated steel sheets 11 by the radialexpansion of the sleeve portion 80a of the open mandrel 80, and furtherpresses the inner peripheral surface of the central hole of thelaminated steel sheets 11 outward in the radial direction. For example,when a stainless steel is used for the sleeve portion 80a of the openmandrel 80, a linear expansion rate of the stainless steel is 16.4×10⁻⁶,whereas a linear expansion rate of the material constituting thelaminated steel sheets 11 is 11.7×10⁻⁶. Thus, supposing that the gapbetween the central hole of the laminated steel sheet 11, having aninner diameter of Φ60, and the sleeve portion 80a is 50 μm, if they areheated to about 200° C. the diameter of the open mandrel 80a increases57 μm even after subtracting the increase in the inner diameter of thelaminated steel sheet 11, so that the gap of 50 μm before heating isexceeded causing the open mandrel 80a to press the inner peripheralsurface of the laminated steel sheets 11 outward in the radial directionby an amount corresponding to the difference of the expansion. As aresult, the inner periphery of the rotor core 12 is aligned by beingpressed by amount of 7 μm.

FIG. 5(d) and FIG. 5(e) schematically illustrate a state that theunevenness on the inner peripheral surface of the rotor core 12 iscanceled by the expansion of the sleeve portion 80a of the open mandrel80. Further, the open mandrel 80 may be of either an oil hydraulic typeor a mechanical type in addition to the type utilizing the thermalexpansion. However, in the case of the thermal expansion type, thedispersion of the partial expansion is relatively small, so that thealignment of the inner periphery can better be accomplished, andfurther, since the structure can be made simple, it is better in termsof the maintenance and durability.

After aligning the inner peripheral surface of the rotor core 12, therotor core 12 is pressed in the axial direction by the hydraulicpressure and the like to remove the gap between the respective laminatedsteel sheet 11 (Step S4), and further the outer peripheral surface ofthe rotor core 12 is temporarily welded (Step S5), thereby preventingmutual friction among the lamination of rotor core 12. The temporarywelding of the outer peripheral surface of the rotor core 12 can beperformed, for example, by axially welding several portions (three tofour portions) of the outer periphery of the rotor core 12 by means of aYAG laser and the like (referred to as a welded portion 86 in FIG.6(c)). The temporary welding can be accomplished by mounting aprocessing nozzle on a processing robot and applying a laser beam havinga capacity of about 500 watt for about three minutes. Further, thefixing of the laminated steel sheets can be made by caulking as well.

FIG. 6(a) and FIG. 6(b) show a state that the open mandrel 80 is cooledand a gap is formed between the outer peripheral surface of the sleeveportion 80a and the inner peripheral surface of the rotor core 12. Inthis state, the laminated rotor core 12 can be taken out from the openmandrel 80. The cooling of the heated open mandrel 80 can be performedby passing a cooling fluid and the like (an oil cooling and a watercooling) through the cooling pipe passage 84. Further, cooling meansother than the cooling pipe passage 84 or a natural cooling not usingthe cooling means may be employed.

Further, FIG. 6(c) shows a state that the open mandrel 80 is taken outfrom the rotor core 12 shown in FIG. 6(a), and FIG. 6(d) shows the openmandrel 80 thus taken out. Further, the temporary welding by the laserbeam or the like is performed on the outer peripheral surface of therotor core 12 shown in FIG. 6(c) to form the welded portion 86.

In process B, following the completion of the process A, the rotor core12 is pre-heated for casting (Step S6). The pre-heating can beperformed, for example, by high frequency induction heating means.

After pre-heating the rotor core 12 in the process B, the die casting isperformed for the rotor core 12 by the conductor casting apparatus 10 inthe process C. The process C will be described below with reference toFIG. 7.

First, in order to transfer the rotor core 12 heated in the process B tothe conductor casting apparatus 10, the simple mandrel 54 having theform shown in FIG. 7 is mounted on the rotor core 12. The simple mandrel54 is provided with a sleeve portion 54a having an outer diametercapable of being inserted into the central opening 50 of the rotor core12, a base 58 with a shoulder portion for holding the rotor core 12 bybeing brought into contact with the lower end portion of the rotor core12, and a supporting portion 56 capable of being used for transferringonly the simple mandrel 54 or the simple mandrel 54 mounted on the rotorcore 12. Mounting the rotor core 12 on the simple mandrel 54 can beaccomplished by inserting the sleeve portion 54a of the mandrel into thecentral opening 50 of the rotor core 12 by using the support tool 56 andthe like. Further, by using the supporting portion 56 and the like, therotor core 12 can be transferred together with the simple mandrel 54.

In the conductor casting apparatus 10, the casting mold 18 is opened,and the cylinder 73 of the holding portion 70 is retreated so that thecup 72 is disposed in the retreated position. Next, the rotor core 12held by the simple mandrel 54 is transferred to the casting mold 18 andis axially vertically mounted on the front end portion of the coresupporting rail 34 of the movable mold 26. In this state, the movablemold 26 is moved to be assembled to the fixed mold 24, whereby the rotorcore 12 is housed within the recess portion 14, and the rotor core 12 isinserted into the recess portion 14 of the fixed mold 24 in accordancewith the motion of the movable mold 26. Then, the rotor core 12 ispushed by the wall of the recess portion 14 of the fixed mold 24 so asto be guided on the core supporting rail 34. Further, by completelyassembling the movable mold 26 to the fixed mold 24, the rotor core 12is inserted into the recess portion 14 of the movable mold 26 (Step S7;FIG. 7(c)).

After the movable mold 26 is assembled to the fixed mold 24 and therotor core 12 is housed within the recess portion 14, the cylinder 73 isadvanced (descended) so that the rotor core 12 is fixed between the cup72 and the core supporting rail 34. In this case, when the stroke of thecylinder 73 is set to be equal to the shortest axial length of the rotorcores 12, both the metal mold and the mandrel can be one kind withrespect to the rotor core 12 whose axial length is variable. FIG. 2(a)shows the case that the axial length of the rotor core 12 is relativelylong, and FIG. 2(b) shows the case that the axial length of the rotorcore 12 is relatively short. By setting the stroke of the cylinder 73 tobe capable of adapting a relatively short axial length of the rotor core12 as in FIG. 2(b), the casting can be performed with the same structureirrespective of the axial length of the rotor core 12.

In this state, the injector front of the casting machine such as the diecasting machine and the like is mounted into the receiving portion 28(FIG. 1) so that the molten metal can be poured into the sprue 16. Themolten metal poured under a predetermined pressure flows into the firstend ring cavity 64 through the runner 20 and fills the conductor formingcavity within the plurality of slots 44 of the rotor core 12. In thiscase, the gas within the conductor forming cavity escapes from thecasting mold 18 through the air vent and the chill vent. In this case, aplurality of air vents and chill vents (the first air vent 15, thesecond air vent 17, the first chill vent 30 and the second chill vent31) provided along the axial length of the rotor core 12 in the axialdirection efficiently allow the gas to escape even in the case ofcasting of the rotor core 12 having a different axial length. Further,when the vacuum pump is connected to the chill vent to draw the gaswithin the metal mold, the casting with less blowholes can be obtained.The molten metal fills the conductor forming cavity within the pluralityof slots 44 and, thereafter, flows into the second end ring cavity 66(Step S8; FIG. 7(c)).

After the plurality of conductor rods 46 and the pair of end ring 48 ofthe rotor core 12 are formed, the cylinder 73 is retreated (ascended) soas to separate the cup 72 from the rotor core 12. Further, the movablemold 26 is moved to open the casting mold 18, and the pushing sheet 40is operated to push out the rotor core 12 to the front end portion ofthe core supporting rail 34 by means of the pushing pin 42 (FIG. 7(d)).

Thereafter, the gate portion 60 at which one of the end ring 48 and themolten metal solidified within the molten metal passage 20 are connectedis cut to be separated (FIG. 7(e)), and the simple mandrel 54 is pulledout from the rotor core 12 (Step S9 and FIG. 7(f)). This will completethe forming of the conductor of the rotor. The drawn-out simple mandrel54 is reused of forming the conductor of the next rotor core 12.

Since the simple mandrel 54 can be reused by rotation irrespective ofthe axial length of the rotor core 12, it is not necessary to preparemany kinds of mandrels in accordance with various axial lengths of therotor core 12, and, further, the necessary number thereof can beminimized in accordance with the cycle for casting operation.

As described above, the holding portion 70 provided in the conductorcasting apparatus 10 adjusts the stroke of the cylinder 73 correspondingto the difference in the axial dimension of the rotor core 12. Next,another means for corresponding to the difference in the axial dimensionof the rotor core 12 will be described below with reference to FIG.8(a), FIG. 8(b), FIG. 9(a) and FIG. 9(b). In this case, only theportions different from the structure explained in the embodimentmentioned above will be described, and the explanation of the commonportions will be omitted.

In the embodiment shown in FIG. 8(a) and FIG. 8(b), the cups 72differing in axial length are used, and replaced according to the axiallength of the rotor core 12, thereby making it possible to adjust therotor core 12 towards the direction of the end portion. In the casewhere the axial dimension of the rotor core 12 is long, as shown in FIG.8(a), the cup 72 having a shorter axial dimension is used. In contrast,in the case where the axial dimension of the rotor core 12 is short, asshown in FIG. 8(b), the cup 74 having a longer axial dimension is used.In this manner, by using, for the holding portion 70, the cups 72 and74, each having the axial dimension in correspondence to the axiallength of the rotor core 12, the same casting apparatus can be used forcasting even when the axial length of the rotor core 12 is changed.

In the embodiment shown in FIG. 9(a) and FIG. 9(b), a plurality ofspacers 71 and 75, each differing in axial dimension are provided, and aspacer in correspondence to the axial dimension of the rotor core 12 isselected from among them. In the case that the axial dimension of therotor core 12 is long, as shown in FIG. 9(a), the spacer 71 having ashorter axial length is used. In contrast, in the case that the axialdimension of the rotor core 12 is short, as shown in FIG. 9(b), thespacer 75 having a longer axial dimension is used. In this manner, byselectively using the spacers 71 and 75, each having the axial dimensionin correspondence to the axial length of the rotor core 12, the sameconductor casting apparatus can be used for casting even when the axiallength of the rotor core 12 is changed.

The spacers 71 and 75 in the embodiment of FIG. 9(a) and FIG. 9(b)partly project on the side facing to the rotor cores 12 and 13 to formthe projecting portion and the shoulder portion. The projecting portionhas a diameter substantially equal to the inner diameter of the rotorcores 12 and 13, and the spacers 71 and 75 and the rotor cores 12 and 13can be positioned by inserting the projecting portion into the spacedefining the inner diameter of the rotor cores 12 and 13 and bringingthe shoulder portion into contact with the end surface of the rotorcores 12 and 13. Further, the rotor core and the spacer can be setsimultaneously within the casting mold by sliding the rotor cores 12 and13 and the spacers 71 and 75 together on the core supporting rail aftermounting the spacers 71 and 75 on the rotor cores 12 and 13 disposed onthe core supporting rail. The same effect can be obtained by changingthe combination of both the cup and the spacer as well as changing onlyone of the cup 72 or 74 and the spacer 71 or 75.

Further, the conductor casting apparatus 10 can be used for casting arotor provided with a balance ring. The casting of the rotor providedwith the balance ring will be described below with reference to FIG. 10.

For casting this rotor the spacer 71 is used in the same manner as inthe case shown in FIG. 9(a). However, the spacer 71 used here has alarger axial length of the projecting portion than that of the spacershown in FIG. 9(a) so as to hold a balance ring 92 between the shoulderportion of the spacer 71 and the upper end surface of the rotor core 12.In FIG. 10, the spacer 71 temporarily fixes the balance ring 92 to therotor core 12 by holding the balance ring 92 against the rotor core 12,using the extended portion of the projecting portion. Further, a lowerbalance ring 92' is inserted into the sleeve portion 54a of the simplemandrel 54 and received by the base 58 so as to be fixed. When themolten metal is filled in a state that the balance ring 92 istemporarily fixed to the rotor core 12, the balance ring 92 is fixed tothe rotor core 12 simultaneously with the conductor casting.

Although holding portion 70 mentioned above employs the single cylinder73, a double cylinder may be employed by adding an additional cylinderfor localized application of pressure. FIG. 11 is a diagram forexplaining the holding portion 70 using the double cylinder. Further,here, only the things different from the structure explained in thepreceding embodiment will be described, and the explanation of thecommon things will be omitted.

The holding portion 70 shown in FIG. 11 has both a holding means forholding the rotor core 12 at a predetermined position within the recessportion 14 against the filling pressure of the molten metal and locallypressing cup for locally applying pressure to the molten metal filled inthe conductor forming cavity (the plurality of slots 44 in the rotorcore 12) independently from the filling pressure.

The holding portion 70 is supported at the upper end (on the sideopposite to the sprue) of the movable mold 26, and comprises a firstcylinder 77, a fixing cup 76 connected to the first cylinder 77, asecond cylinder 79 and a locally pressing cup 78 connected to the secondcylinder 79. The fixing cup 76 fixes the rotor core 12 within the recessportion 14, and the locally pressing cup 78 additionally applieslocalized press to the molten metal filled in the second end ring cavity66.

When the first cylinder 77 is driven and the work fixing cup 76 isadvanced (descended), the axial end surface thereof is brought intocontact with the axial end surface of the rotor core 12 within therecess portion 14. As a result, the rotor core 12 is held at apredetermined position within the recess portion 14 between the workfixing cup 76 and the core supporting rail 34. Further, when the secondcylinder 79 is driven at a proper timing so as to advance (descend) thelocally pressing cup 78, the axial end surface of the locally pressingcup 78 compress the molten metal filled in the second end ring cavity66. As a result, the second end ring corresponding to the end ringformed on the side opposite to the sprue is prevented from forming theblowholes.

According to the embodiments of the invention, it is not necessary tofix both ends of the lamination of steel sheets by the fastening member,so that the provision of the fastening member and its forming processcan be omitted.

In the apparatus for casting the conductor of the cage rotor of theinduction motor shown in FIG. 11, the mandrel (the simple mandrel 54) inthe form shown in FIG. 7 is used as the mandrel. However, in place ofthis simple mandrel, as shown in FIG. 12, a mandrel 57 (hereinafterreferred to as the conventional mandrel) comprising a sleeve 53 havingan axial length equal to that of the rotor core 12 and a diametersubstantially equal to the inner diameter of the rotor core, and anupper cap 51 and lower cap 55 respectively mounted on the upper end andthe lower end of the sleeve 53 may be employed.

An apparatus for casting the conductor of the cage rotor of theinduction motor using the conventional mandrel 57 is shown in FIG. 12.The conductor casting apparatus is provide with the holding portion 70employing the double cylinder (the first cylinder 77 and the secondcylinder 79) in the same manner as the conductor casting apparatus shownin FIG. 11, and is suitable particularly for casting a rotor for highspeed rotation . The operation in the case that the conventional mandrel57 is used for casting by the conductor casting apparatus is the same asthe case shown in FIG. 11, so that the explanation thereof is omitted.

FIG. 12 shows the embodiment in which the conventional mandrel 57 isused in the cage rotor conductor casting apparatus including the holdingportion 70 provided with the double cylinder, and an embodiment in whichthe conventional mandrel 57 described above is used in the cage rotorconductor casting apparatus including the holding portion 70 providedwith the single cylinder 73 is shown in FIG. 13(a) and FIG. 13(b).

In the case shown in FIG. 13(a), the axial length of the rotor core 12is large, so that the cup 72 having a shorter axial length is used and,while in the case shown in FIG. 13(b), the axial length of the rotorcore 12 is small, so that the cup 72 having a longer axial length isused. In the case that the conventional mandrel 57 is used, when thesleeve 53 of the mandrel is formed by using a material such as astainless steel and the like, the same effect (aligning the innerdiameter of the core) as the open mandrel 80 described can be obtained,and, in the case of using the rotor core 12 having a different axiallength, as in the same manner as the embodiment shown in FIG. 2(a) andFIG. 8(a), casting operation can be carried out by changing the strokeof the cylinder or the axial dimension of the cup. Since the operationin this case is the same as the operation in the conductor castingapparatus explained with reference to FIG. 11, the explanation thereofis omitted.

We claim:
 1. An apparatus for casting a conductor of a cage rotor of aninduction motor, comprising:a casting mold provided with a recessportion for receiving a rotor core formed by piling up steel sheets andrestraining a motion of the rotor core in a radial direction, and aholding portion which moves toward an end surface of the rotor corehoused in the recess portion of said casting mold by drive means andacts on the end surface so as to fix the axial motion of the rotor core,wherein molten metal is supplied into a plurality of slots formed in therotor core fixed by said recess portion and said holding portion so asto form a plurality of conductor rods and a pair of end ringscommunicating the ends of the conductor rods with one another, wherein amoving amount of said holding portion can be adjusted in correspondenceto an axial length of the rotor core.
 2. An apparatus for casting aconductor of a cage rotor of an induction motor, comprising:a castingmold provided with a recess portion for receiving a rotor core formed bypiling up steel sheets and restraining a motion of the rotor core inradial direction, and a holding portion which moves toward an endsurface of the rotor core housed in the recess portion of said castingmold by drive means and acts on the end surface so as to fix the axialmotion of the rotor core, wherein molten metal is supplied into aplurality of slots formed in the rotor core fixed by said recess portionand said holding portion so as to form a plurality of conductor rods anda pair of end rings communicating the ends of the conductor rods withone another, wherein only said holding portion is made replaceable, andthe casting mold is made common.
 3. An apparatus for casting a conductorof a cage rotor of an induction motor, comprising:a casting moldprovided with a recess portion for receiving a rotor core formed bypiling up steel sheets and restraining a motion of the rotor core in aradial direction, and a holding portion which moves toward an endsurface of the rotor core housed in the recess portion of said castingmold by drive means and acts on the end surface so as to fix the axialmotion of the rotor core, wherein molten metal is supplied into aplurality of slots formed in the rotor core fixed by said recess portionand said holding portion so as to form a plurality of conductor rods anda pair of end rings communicating the ends of the conductor rods withone another, wherein said holding portion comprises a cylinder movingtoward said end surface of the rotor core by means of said drive meansand a pressing member connected to the cylinder and acting on said endsurface of the rotor core by a motion of the cylinder, and said pressingmember is selected so that it may have an axial dimension correspondingto the axial length of the rotor core and is mounted on said cylinder.4. An apparatus for casting a conductor of a cage rotor of an inductionmotor as recited in claim 3, wherein said pressing member is formed of acup-shaped member and an end surface of the cup-shaped member directlyacts on an end surface of the rotor core.
 5. An apparatus for casting aconductor of a cage rotor of an induction motor as recited in claim 3,wherein said pressing member comprises a cup-shaped member and a spacerwhich is inserted between an end surface of the cup-shaped member and anend surface of the rotor core, and wherein the spacer having an axialdimension in correspondence to the axial length of the rotor core isselected.
 6. An apparatus for casting a conductor of a cage rotor of aninduction motor as recited in claim 1, wherein said holding portioncomprises a first cylinder, a first cup connected to the first cylinder,a second cylinder operating independently of the first cylinder and asecond cup connected to the second cylinder, and wherein the first cupacts on an end surface of the rotor core housed in the recess portion ofthe casting mold, and the second cup additionally applies pressure tothe molten metal filled in the end ring cavity formed in the sideopposite to the sprue.
 7. An apparatus for casting a conductor of a cagerotor of an induction motor as recited claim 1, wherein, as anaccessory, there is provided a first mandrel whose thermal expansionrate is larger than that of the steel sheets constituting the rotorcore, whose axial dimension is not shorter than that of the rotor coreand which has a sleeve portion with a heating means provided insidethereof, andwherein said first mandrel is heated by the heating meansafter being inserted into the central opening of the rotor core butprior to being received within the recess portion of the casting mold,whereby an unevenness of the inner periphery of the central opening ofthe rotor core is leveled by the thermal expansion of the sleeve.
 8. Anapparatus for casting a conductor of a cage rotor of an induction motoras recited in claim 1, wherein, as an accessory, there is provided asecond mandrel comprising a shaft portion having an outer diameterallowable for being inserted into the central opening of the rotor coreand an end portion having a supporting portion provided at an end of theshaft portion and a shoulder portion having a diameter larger than theouter diameter of the shaft portion disposed on the other end of theshaft portion, andwherein, when the second mandrel is inserted into thecentral opening of the rotor core received into the recess portion ofthe casting mold and the casting is completed, the rotor core is removedout of the recess portion of the casting mold together with the secondmandrel by being held by the supporting portion of the second mandrel.9. An apparatus for casting a conductor of a cage rotor of an inductionmotor as recited in claim 1, wherein said casting mold is provided witha plurality of air vents in an axial direction on the inner surface ofthe recess portion which houses the rotor core.
 10. A method for castinga conductor of a cage rotor of an induction motor, comprising stepsof;(a) laminating steel sheets to a predetermined thickness by passing acentral opening of the steel sheets through a sleeve portion of amandrel, (b) leveling an unevenness of inner periphery of a centralopening of the laminated steel sheets occurred during laminating processby the effect of thermal expansion of said sleeve resulting from beingheated, (c) pressing said laminated steel sheets in the axial directionand temporarily fixing the outer periphery thereof so as to form therotor core, (d) housing said rotor core in the recess portion of thecasting mold formed in the conductor casting apparatus, (e) adjusting anaxial dimension of the holding portion or a stroke of the holdingportion acting on an axial end of said rotor core, to axial dimension ofsaid rotor core, and (f) forming a plurality of conductor rods and apair of end rings communicating ends of the conductor rods with oneanother by supplying molten metal into a plurality of slots formed inthe rotor core which is held by said holding portion.
 11. A method forcasting a conductor of a cage rotor of an induction motor as recited inclaim 10, wherein added between said Steps (c) and (d) is a step ofinserting a mandrel provided with a shaft portion having an outerdiameter allowable for being inserted into the central opening of therotor core, an end portion with a supporting portion disposed at an endof the shaft portion and a shoulder portion having a diameter largerthan the outer diameter of said shaft portion disposed at the other endof the shaft portion, andand further added after said Step (f) is a stepof removing, by using said mandrel, the rotor, with which a plurality ofconductor rods and a pair of end rings are formed in the rotor core,from the casting mold.